1. Field of the Invention
This invention relates to a photoresist stripping liquid composition and a method of stripping photoresists using the composition. More particularly, the invention relates to a liquid composition excellent not only in stripping photoresist layers and the deposition (residue) that occurs after the etching or ashing step but also in protecting substrates from corrosion having metallic, inorganic or like films formed on them. The invention also relates to a method of stripping photoresists using the composition. The invention is suitable for use in the fabrication of semiconductor devices such as ICs and LSIs, as well as liquid-crystal panel apparatus.
2. Description of Relevant Art
The fabrication of semiconductor devices such as ICs and LSIs, as well as liquid-crystal panel apparatus, comprises the steps of forming conductive metallic layers such as a tin oxide film and insulating layers such as an SiO.sub.2 film on a substrate by CVD or any other suitable techniques; applying a uniform photoresist coating over the metallic layers and insulating layers; performing selective exposure and development to form a photoresist pattern; selectively etching the metallic layers and insulating layers using the photoresist pattern as a mask to form a microcircuit; and removing the unwanted photoresist layer with a liquid stripper. Other examples of the conductive metallic layers include those of aluminum (Al), aluminum alloys such as aluminum-silicon (Al-Si), aluminum-copper (Al-Cu) and aluminum-silicon-copper (Al-Si-Cu), titanium (Ti), titanium alloys such as titanium nitride (TiN) and titanium-tungsten (TiW), and copper (Cu). Also in use are inorganic films such as an amorphous silicon (a-Si) film and a polysilicon (poly-Si) film. These metallic, insulating and inorganic films are formed in one or more layers on the substrate.
While various liquid compositions have heretofore been used to strip photoresist layers, the use of liquid systems incorporating alkanolamines was recently proposed (as in Unexamined Published Japanese Patent Applications Nos. 49,355/1987 and 208,043/1988).
In the current fabrication process of semiconductor devices and liquid-crystal devices, dry etching, ashing, ion implantation and other post-treatments are applied to photoresist films, and that it becomes necessary to strip thusly treated photoresist films. Due to those post-treatments, the photoresist films become modified or deteriorated in nature. With the recent increase in the strictness of the conditions for these post-treatments, the nature of the deteriorated photoresist films tends to become inorganic than organic and, as a result, the liquid strippers using alkanolamines have turned out to be inadequate for the purpose of stripping the deteriorated photoresist films.
More recently, liquid compositions containing hydroxylamines have been proposed as systems capable of more efficient stripping of deteriorated photoresist films. For example, Unexamined Published Japanese Patent Application No. 289,866/1992 describes a photoresist stripping liquid composition containing both hydroxylamines and alkanolamines, and Unexamined Published Japanese Patent Application No. 266,119/1994 describes a photoresist stripping liquid composition containing not only hydroxylamines and alkanolamines but also a chelating agent (corrosion inhibitor) such as catechol.
These liquid compositions containing hydroxylamines have a greater ability to strip the deteriorated photoresist films than the liquid strippers containing alkanolamines. However, they cause another problem in that substrates having deposited films of Al or Al alloys such as Al-Si and Al-Si-Cu, or pure titanium (Ti) are corroded.
To avoid these problems, several proposals have been made as exemplified by the teaching of Unexamined Published Japanese Patent Application No. 96,911/1997, which discloses photoresist stripping liquid compositions comprising hydroxylamines, water, amines having a specific acid dissociation constant, water-soluble organic solvents and a specified amount of corrosion inhibitors. These compositions are excellent particularly in the capability of stripping deteriorated films and exert good corrosion-inhibiting effects on substrates having films of Al, Al alloys or pure titanium (Ti) formed thereon.
However, none of these photoresist stripping liquid compositions containing hydroxylamines have been studied for their ability to prevent corrosion of substrates having amorphous silicon, polysilicon and other inorganic films that find increasing use today, particularly in the field of liquid-crystal devices. Among such inorganic films, the polysilicon film has high mobility and is extensively used in liquid-crystal panels and other devices with a view to reducing their size. An increasing demand has therefore arisen for a photoresist stripping liquid composition that has high ability to prevent the corrosion of substrates having polysilicon and other inorganic films. In other words, it has been desired to develop a photoresist stripping liquid composition that will not corrode those substrates having various kinds of metallic layers and inorganic films for use in ICs and liquid-crystal panels and which are excellent in their ability to strip deteriorated photoresist films, as well as deposition (residue) that occurs after the etching or ashing step.
The present invention has been accomplished under these circumstances and has as an object providing a liquid composition excellent not only in stripping photoresist films and the deposition (residue) that occurs after the etching or ashing step but also in protecting substrates from corrosion even if they have metallic, inorganic or like films formed on them. Another object of the invention is to provide a method of stripping photoresists using the composition.